The present invention relates to ink jet recording devices and, more particularly, to a system for detecting the presence of an ink supply container and also for detecting when the level of ink in the container is at or below a predetermined level.
Ink jet recording devices eject ink onto a print medium such as paper in controlled patterns of closely spaced dots. To form color images, multiple groupings of ink jets are used, with each group being supplied with ink of a different color from an associated ink container.
Thermal ink jet printing systems use thermal energy selectively produced by resistors located in capillary filled ink channels near channel terminating nozzles or orifices to vaporize momentarily the ink and form bubbles on demand. Each temporary bubble expels an ink droplet and propels it toward a recording medium. The printing system may be incorporated in either a carriage type printer or a pagewidth type printer. A carriage type printer generally has a relatively small printhead containing the ink channels and nozzles. The printhead is usually sealingly attached to an ink supply container and the combined printhead and container form a cartridge assembly which is reciprocated to print one swath of information at a time on a stationarily held recording medium, such as paper. After the swath is printed, the paper is stepped a distance equal to the height of the printed swath, so that the next printed swath will be contiguous therewith. The procedure is repeated until the entire page is printed. In contrast, the pagewidth printer has a stationary printhead having a length equal to or greater than the width of the paper. The paper is continually moved past the pagewidth printhead in a direction normal to the printhead length at a constant speed during the printing process. Moving carriage type ink jet printers must either carry the ink container along with the printhead or provide a flexible ink supply line between the moving printhead and a stationary ink container. Pagewidth printers have an ink supply container located outside the print zone and directly connected to the printbar ink channels.
For either a partial width printhead on a moving carriage or for a pagewidth printbar, it is desirable to have a low ink level warning to alert a user to replace or refill the ink container so that the ink does not run out during a print job. Presently, for some applications (such as plotting), some users choose to install new print containers prior to starting an extensive printing job because it is less costly to replace a questionable container rather than lose one or more colors in the output prints. It is also important to ensure that the ink supply container is in the proper location; e.g., fluidly connected to the associated printhead. In some instances, an out of ink container may be removed but a replacement container neglected to be inserted. Printer operation with the container removed could potentially damage the associated printhead.
Various prior art methods and devices are known for detecting reduced levels of ink in an ink supply container. U.S. Pat. No. 4,342,042 discloses an ink sensing system which includes output from an LED sensor reflected from a flexible membrane which serves as the upper surface of an ink supply reservoir. The membrane contracts as the ink level is depleted, and the LED sensor detects the contraction and generates a low ink level signal.
U.S. Pat. No. 5,079,570 provides a method for detecting ink levels in an ink cartridge where the ink is supplied from a foam reservoir. A binary fluidic indicator is fluidly coupled with the foam reservoir and is triggered when the fluid level in the foam reaches a certain prescribed level.
U.S. Pat. No. 5,289,211 discloses a low ink detecting system which includes a pair of electrodes immersed in the ink impregnated foam reservoir. The electrodes are connected to a bridge circuit which measures the electrical resistance of the ink between the two electrodes.
U.S. Pat. No. 5,414,452 uses a logic circuit which counts the number of drops expelled and compares the instant number with the maximum number of drops equivalent to a known value of ink in the ink reservoir.
U.S. Pat. No. 5,434,603 discloses a visual indicator system where sidewalls of the reservoir retreat inwardly during ink depletion changing the orientation of indicator stripes and modifying the color visible to an observer through a window.
U.S. Pat. No. 5,386,224 places a level sensing probe into the ink supply and senses electrical conductivity changes of the ink.
U.S. Pat. No. 5,136,305 discloses a low ink detecting system wherein a thermistor is placed in the ink supply and periodically energized. The temperature rise of the ink is measured and compared with pre-established values to determine the ink depletion state of the reservoir.
U.S. Pat. No. 4,639,738 discloses a detection system which incorporates detection ports in the cartridge for detecting pressure conditions in the top and bottom of the cartridge. The ports are coupled to a pressure differential sensor that signals a refill condition.
Japanese publication 5-332812 describes a low ink detection system wherein the cartridge has a transparent optical path member installed in an opening of a surface of an ink storage tank. An LED emits a beam of light which is guided into the ink tank and reflected back to a sensor to provide an indication of low ink levels.
Some of the prior art references are relatively expensive relying on measurement and detection of ink conductivity or drop detecting circuitry. Further, none of the prior art references includes means for insuring that the ink tank is in proper position before beginning the ink level sensing operation.
It is, therefore, one object of the present invention to provide a detection system which confirms the proper installation of an ink container supplying ink to an associated printhead.
It is another object to present a detection system for detecting a low level of ink in the ink container and for providing a low ink level warning signal.
Another object of the invention is to provide an ink supply container which is constructed so as to enable an inexpensive optical detection system which performs both the ink container detection as well as the low ink level detection function.
In the present invention, and in an exemplary embodiment, a thermal printer is disclosed which includes a printhead for printing on a recording medium in response to image drive signals. Ink is supplied to the printhead from an ink container which is fluidly connected to the printhead. The printhead and container are mounted on a scanning carriage which moves back and forth across a print zone, the printhead ejecting ink droplets from nozzles to form an image on the recording medium. An optical system comprising two light sources and a light detector is fixedly located along the path of travel of the carriage and positioned so that light from the light source is directed into the ink container as it is positioned opposite the optical system. The ink container has optical light directing elements formed in a transmissive wall. Light from the light sources are directed into and onto the container through the transparent wall and, sequentially, onto the optical elements. In one embodiment, the light directing elements are reflective prisms; reflections of light from these elements, or lack thereof, is sensed by a common photosensor to provide signals representing the presence or absence of the container and the level of ink remaining in the container.
More particularly, the present invention relates to a sensing system for detecting the presence of an ink container and the level of ink therein comprising:
first light directing means operatively connected to said container,
a first light source having output beams directed toward said light directing means when in a container detect mode,
photosensor means for detecting the presence or absence of light directed from said light directing means and for generating an output signal indicative thereof,
second light directing means operatively connected to said container,
a second light source having output beams directed toward said second light directing means when in a low ink level detect mode and
photosensor means for detecting light directed from said second light directing means, the level of detected light and hence the level of the photosensor output being representative of the presence or absence of ink adjacent the interior surface of the second light directing means.
Further, the present invention relates to a method for detecting the presence or absence of a cartridge mounted on a movable carriage and used in an ink jet printer and the level of ink in an ink container associated with said cartridge including the steps of:
directing a beam of light into an optical sensing station,
moving said carriage into said optical sensing station so that a portion of said cartridge, if present, intercepts said light beam,
sensing the presence or absence of light redirected back from said portion and
generating a signal representative of the presence or absence of a cartridge.
The invention also relates to a system for sensing the presence or absence of an ink cartridge in an ink recording device, said cartridge including a printhead and an ink container for supplying ink to said printhead, said system including:
at least one printhead for printing each of a first color onto a recording medium,
an associated ink supply container for providing ink of said first color to said printhead, said container having at least a partially transparent section of a wall, said wall having at least a reflective member associated therewith,
means for moving said cartridge along a scan path,
an optical sensing station located along said scan path and comprising a light source and a photosensor,
means for moving said cartridge into said station so that, if said cartridge is physically present the reflective member is opposite said light source output and
means for energizing said light source, said photosensor either sensing a light source output beam reflected from said reflective member thereby indicating the presence of a cartridge or sensing lack of an reflected light indicating the absence of a cartridge.